The present application generally relates to methods and apparatus for transfer of films from one or more substrates to another, where the film to be transferred is patterned during the transfer step.
Since the first isolation of graphene in 2004 , interest in the material has surged in the research community and more recently in industry as the first commercial ventures in graphene production and applications have emerged. Graphene is a single atom thick sheet of carbon atoms packed in a honeycomb lattice that has unique properties owing to its two-dimensional geometry and aromatic chemical structure. The unique band structure of this material shows a linear dispersion relation at low energies, allowing the holes and electrons to have zero effective mass and behave like relativistic particles. This leads to impressive electrical properties, such as measured mobilities of 200,000 cm2/V-s and ballistic transport on the micrometer scale at room temperature. Additionally, the superior tensile strength of the material allows for high electrical performance even under bending and deformation. Due to these fantastic properties, there has been great interest for applications in high performance nanoelectronics, flexible electronics, and environmental/biological monitoring applications.
Graphene can be grown in high quality sheets on catalytic metal by chemical vapor deposition at industrial scale, presenting an opportunity for graphene commercialization that is being pursued by multiple companies. In conventional approaches, graphene is coated with a thin polymer layer (e.g., polymethylmethacrylate—PMMA) to provide mechanical stability and then removed from a copper growth substrate for transfer onto another substrate as a full sheet that may then be patterned into electrical devices, etc. There are several disadvantages of this—e.g., the graphene can be wrinkled during the transfer process since the PMMA layer is very thin and flexible; the graphene can be contaminated with PMMA residue after cleaning; and the subsequent patterning process can expose the graphene to chemical contamination. Each of these causes the physical properties (including the carrier mobility) of the graphene to degrade. Processes are needed for transferring graphene from growth substrates to other surfaces while protecting the beneficial properties of the material so that it may be used in commercial devices.
Thus, there is a need for processes that enable transfer of graphene from growth substrates to other surfaces. There are sets of materials “beyond graphene” (e.g., few-layer graphene, boron nitride, molybdenum disulfide, other transition metal dichalcogenides, and the like) with similar needs for advanced methods of film transfer. The instant disclosure is directed to these and other important needs.